Priority is claimed to Patent Application number 2001-29253 filed in Rep. of Korea on May 26, 2001, herein incorporated by reference.
1. Field of the Invention
The present invention relates to a method for fabricating a semiconductor light emitting device, and more particularly, to a method for fabricating a semiconductor light emitting device by which an n-type electrode can be effective formed by processing the bottom of a substrate.
2. Description of the Related Art
The need for high-density information recording has increased the demand for semiconductor visible-light emitting devices. In particular, the market release of high-density optical recording media such as digital versatile discs (DVDs) has boosted the need for visible-light emitting laser diodes. There are available a variety of compound semiconductor laser diodes (LDs) capable of visible laser emission. In particular, III-V nitride compound semiconductor laser diodes, a direct transition type that ensures high-efficiency laser oscillation, have received considerable attention because of the ability to emit blue laser light. Semiconductor-based blue light emitting diodes (LEDs) also are attractive because they can be applied to lightening devices.
In general, III-V nitride compound semiconductor light emitting devices are formed on gallium nitride (GaN) substrates to improve their light emitting characteristics.
FIG. 1 is a sectional view of a conventional GaN-based LED formed on a GaN substrate. Referring to FIG. 1, an n-doped GaN layer 4, an active layer 6, and a p-doped GaN layer 8 are sequentially formed on a GaN substrate 2. A transparent p-type electrode 10 is formed on the p-doped GaN layer 8, and a bonding pad 12 is formed in a predetermined region of the p-type electrode 10.
In FIG. 1, reference numeral 14 denotes an n-type electrode formed on the bottom of the GaN substrate 2. The n-type electrode 14 is attached to the bottom of the GaN substrate 2 after grinding, lapping, or polishing the bottom of the GaN substrate 2 to a thickness by which a resulting light emitting device can still be supported. During this polishing step, the bottom of the GaN substrate 2 is damaged, thereby resulting in a damaged layer 16 on the bottom of the GaN substrate 2. As a result, the n-type electrode 14 is attached to the damaged layer 16.
Accordingly, the properties of the resulting light emitting device degrade due to poor attachment of the n-type electrode 14 to the GaN substrate 2. For example, a relative light emitting efficiency with respect to the voltage applied to the n-type electrode 14 may be lowered. Also, the light emission during operation of the light emitting device becomes poor, thereby shortening the lifespan.
FIG. 2 is a sectional view of a conventional GaN laser diode (LD) formed on a GaN substrate. Referring to FIG. 2, an n-doped GaN layer 24, an n-doped AlGaN/GaN cladding layer 26, an n-doped GaN waveguide layer 28, an InGaN active layer 30, a p-doped GaN waveguide layer 32, a p-doped AlGaN/GaN cladding layer 34, and a p-doped GaN layer 36 are sequentially formed on a GaN substrate 22. The p-doped AlGaN/GaN cladding layer 34 has a ridge to be used as a current path, and the p-doped GaN layer 36 is formed on the ridge. A passivation layer 38 is formed on the p-doped AlGaN/GaN cladding layer 34 having the ridge to expose a current path region of the p-doped GaN layer 36. A p-type electrode 40 is formed on the passivation layer 38 in contact with the exposed region of the p-doped GaN layer 36. An n-type electrode 42 is formed on the bottom of the GaN substrate 22 by the same process as for the n-type electrode 14 of the LED shown in FIG. 1. As a result, a damaged layer 44 is formed on the bottom of the GaN substrate 22 of the LD, and the n-type electrode 42 is formed on the damaged layer 44, thereby causing similar problems as those occurring in the LED.
In general, when forming a III-V nitride-based compound semiconductor light devices on a GaN substrate, the bottom of the substrate is subjected to mechanical polishing to reduce the thickness of the substrate for the purpose of heat dissipation and device isolation for LEDs, and cleaved plane formation for LDs. However, during this polishing process, a damaged layer is formed on the bottom of the substrate, as described above, so that attachment of the n-type electrode to the bottom of the GaN substrate becomes unstable, thereby degrading device properties.
To solve the above-described problems, it is an object of the present invention to provide a method of fabricating a semiconductor light emitting device by which formation of a damaged layer on the bottom of a substrate on which a light emitting device is formed, in processing the bottom of the substrate is prevented so that device properties are improved.
To achieve the object of the present invention, there is provided a method for fabricating a semiconductor light emitting device, the method comprising: forming a light emitting construct including a p-type electrode on a n-type substrate; etching a bottom surface of the n-type substrate; and forming an n-type electrode on the etched bottom surface of the n-type substrate.
It is preferable that, after forming the light emitting construct and before etching the bottom surface of the n-type substrate, the bottom surface of the n-type substrate is mechanically polished. It is preferable that the light emitting construct is for a light emitting diode (LED) or a laser diode (LD).
It is preferable that the bottom surface of the n-type substrate is dry or wet etched. The dry etching may be accomplished by a method selected from the group consisting of chemical assisted ion beam etching (CAIBE), electron cyclone resonance (ECR) etching, inductively coupled plasma (ICP) etching, and reactive ion etching (RIE). Preferably, the dry etching uses Cl2, BCl3 or HBr gas as a main etching gas. In this case, Ar or H2 gas may be used as an additional gas for the drying etching. Preferably, the wet etching is accomplished using a KOH, NaOH, or H3PO4 as an etchant.
In the semiconductor light emitting device fabricating method according to the present invention, the bottom surface of the n-type substrate may be polished by grinding or lapping.
It is preferable that the n-type electrode is formed by at least one material selected from the group consisting of titanium (Ti), aluminium (Al), indium (In), tantalum (Ta), palladium (Pd), cobalt (Co), nickel (Ni), silicon (Si), germanium (Ge), and silver (Ag), and is thermally treated at a temperature of 0-500xc2x0 C.
The n-type substrate is preferably an n-type Group III-V compound semiconductor substrate, more preferably, an n-type GaN substrate.
According to the present invention, formation of a damaged layer in processing the bottom of the GaN substrate can be prevented so that stable attachment of the n-type on the bottom of the GaN substrate is ensured, thereby improving the properties of a light emitting device formed on the GaN substrate.